Mōnth, n.

(mūnth), n. [A-S. mônādh, mônōdh, mônudh, mônādh, from môna, the moon; O. Fries. mônath, Goth. mênôths, O. H. Ger. mânôt, N. H. Ger. monat, Icel. mânadr, mânudr, Sw. mânad, Dan. maaned, D. maand, allied to Gr. μήν, Lat. mensis, Skr. mâs, from mâ, to measure.] One of the twelve portions into which the year is divided; the twelfth part of a year, corresponding nearly to the length of a synodic revolution of the moon; whence the name.

☞ In popular usage, four weeks are called a month, being nearly the length of the lunar month.

Calendar months, the months as adjusted in the common or Gregorian calendar; April, June, September, and November containing 30 days, and the rest, except February, which, in common years, has 28, and in leap years 29.— Lunar month, the period of one revolution of the moon, particularly a synodical revolution; but several kinds are distinguished, as the synodical month, or period from one new moon to the next, in mean length 29d. 12h. 44m. 2.87s.; the nodical month, or time of revolution from one node to the same again, in length 27d. 5h. 5m. 36s.; the sidereal, or time of revolution from a star to the same again, equal to 27d. 7h. 43m. 11.5s.; the anomalistic, or time of revolution from perigee to perigee again, in length 27d. 13h. 18m. 37.4s.; and the tropical, or time of passing from any point of the ecliptic to the same again, equal to 27d. 7h. 43m. 4.7s.— Solar month, the time in which the sun passes through one sign of the zodiac, in mean length 30d. 10h. 29m. 4.1s.